code: def normalize_callback(cb):
      """Normalizes a callback to a tuple"""
      if isinstance(cb, Callback):
          return cb._callback
      elif isinstance(cb, tuple):
          return cb
      else:
          raise TypeError(
              "Callbacks must be either `Callback` or `tuple`"
          )
  
file_path: dask/dask/callbacks.py
imports: from __future__ import annotations
  from collections.abc import Callable
  from contextlib import contextmanager
  from typing import ClassVar
label_desc: Use image node_id 3 for calling a global function with example usage: normalize_callback(cb) and returns: cb, cb